The 18 counties are split into two groups this year - North and South - with the top four from each going through to the quarter-finals. We've put together a team-by-team guide and Mike Atherton has picked out a player to watch for each county.

North Group

Captain: Jim TroughtonOverseas players: Shoaib Malik (Pak), Jeetan Patel (NZ)A controversial 'rebrand' means Warwickshire will morph into the Birmingham Bears in T20 cricket this season. Whatever they are called, an improvement in this format is overdue after three straight group-stage exits, something skipper Troughton has himself admitted. Little has changed personnel wise from 2013, with the recruitment of Pakistan batsman Shoaib Malik the main addition.Athers' one to watch: Chris Woakes - Some eye-catching displays have elevated this all-rounder into England's T20 and 50-over squads so availability will be an issue but expect him to play a match-winning role at some point.

Captain: Wayne MadsenOverseas players: Shivnarine Chanderpaul (WI), Marcus North (Aus)It is nine years since Derbyshire made it out of the group stage, the longest run of any county. They have started the season poorly after being relegated back to Division Two of the County Championship with their top order, skipper Wayne Madsen apart, struggling for runs. Perhaps a change of format will prompt a change of form.Athers' one to watch: Wayne Madsen - After enjoying something of a stellar season in 2013, the skipper will need big contributions from Shivnarine Chanderpaul and Marcus North to steer his side to their first quarter-final since 2005.

Captain: Mark StonemanOverseas player: John Hastings (Aus)In contrast to their three County Championship titles in the last six years, Durham have yet to make much impact in T20 with just one finals day appearance to their name back in 2008. Mark Stoneman has taken on the limited-overs captaincy and the team have once again changed their nickname, this time to the Jets (they have previously been known as the Dynamos and Men in Black). Powerful Australian all-rounder John 'The Duke' Hastings is a useful addition as overseas pro.Athers' one to watch: Mark Stoneman - The signs are that this left-hander is slowly but surely coming of age, suspicions confirmed by his career-best 131 in the Championship against Yorkshire. Could be a breakthrough T20 season.

Captain: Glen ChappleOverseas player: Junaid Khan (Pak)Lancashire have been nearly men in Twenty20 down the years, defeat in the 2005 final to Somerset the closest they have come to lifting the trophy despite making it out of the group stage in eight of 11 years. The addition of Jos Buttler during the winter is a huge upgrade to their batting in this format and there has even been talk of former England all-rounder Andrew Flintoff making a shock comeback. Pakistan left-armer Junaid Khan supplements an already strong seam attack, while Steven Croft could get some leadership opportunities if coach-captain Glen Chapple prefers to oversee things from the dugout.Athers' one to watch: Junaid Khan - His left-arm pace offers something a little bit different. Had a big impact at Old Trafford in 2011 - the only season Lancashire have reached Finals Day in the last six years.

Captain: Josh CobbOverseas players: Ramnaresh Sarwan (WI), Scott Styris (NZ)The only county to win the tournament three times - 2004, 2006 and 2011 - but have struggled since the most recent of those triumphs, winning only six of their 20 matches in the last two years. The old guard have been phased out to make way for a new generation, spearheaded by Josh Cobb, Ned Eckersley and Shiv Thakor. Experienced New Zealand all-rounder Scott Styris has been brought in for the tournament and, by my count, will be appearing for his fifth different county!Athers' one to watch: Josh Cobb - A young and improving captain whose three 40-over hundreds last season provided proof of a growing maturity. Will benefit from having the older heads of Scott Styris and Ramnaresh Sarwan alongside him.

We recall David Willey's matchwinning performance leading Northants to victory over Surrey in last season's flT20 final.

Captain: Kyle CoetzerOverseas players: Richard Levi (SA), Sohail Tanvir (Pak)The defending champions are without last year's skipper Alex Wakely for the entire season due to an Achilles injury. Scotland international Kyle Coetzer takes charge but does not have Australian batsman Cameron White to make his job easier this time round. White's wise counsel and ability to hit long and straight will be missed but the remainder of the side remains intact, although the demands of Division One cricket in the championship and a small squad means a repeat is asking a lot.Athers' one to watch: David Willey - Like his county, has much to live up to after last year's final heroics but should go well again providing he can come through his latest injury problems successfully.

Alex Hales is the only Englishman to have scored a T20 international century

Nottinghamshire Outlaws

Captain: James TaylorOverseas player: Peter Siddle (Aus)The group stage has not been the problem for Nottinghamshire in recent years but they have developed the nasty habit of losing in the quarter-finals, three times in a row and counting. Moving on without David Hussey would leave a hole in the power hitting at most counties but not so at Trent Bridge, where Michael Lumb and Alex Hales - England's preferred opening pair - provide box-office appeal at the top of the order. James Taylor is new to the captaincy but in his favour is a strong squad with depth in all areas. Finals day is the minimum targetAthers' one to watch: Samit Patel - Quite simply a quality all-round player who England appear to have discarded prematurely, although Mick Newell's appointment as selector could offer him a way back in.

Worcestershire Rapids

Captain: Daryl MitchellOverseas players: Colin Munro (NZ), Mitchell McClenaghan (NZ), Saeed Ajmal (Pak)There are several reasons to believe Worcestershire - despite a ridiculous new nickname - could be a surprise package. The recruitment of New Zealand left-arm fast bowler Mitchell McClenaghan, plus the potential for an appearance or two from Pakistan spinner Saeed Ajmal, gives the Rapids a cutting edge to their bowling attack like few others. Add in some power hitting from Gareth Andrew, the all-round excellence of Moeen Ali, plus the shrewd captaincy of Daryl Mitchell and it is hard to see how this side is rated among the worst in the competition by the bookmakers.

Athers' one to watch: Daryl Mitchell - The Royals will need their captain to take his impressive early-season Championship form into the Blast if they are to improve on an underwhelming T20 record.

Yorkshire Vikings

Captain: Andrew GaleOverseas players: Aaron Finch (Aus), Kane Williamson (NZ)Yorkshire's T20 record over the years is surprisingly poor. Losing to Hampshire in the finals day two years ago was followed up in 2013 by a dismal campaign in which they won just two matches. The recruitment of Australian batsman Aaron Finch - one of the most destructive around - is a serious signal of intent. Flying high in the County Championship with one of the deepest squads around.Athers' one to watch: Aaron Finch - No ground is too small for the Australian once he gets going, as his world record 156 against England last summer proved. Bags of T20 experience but form has been mixed for Hyderabad.

South Group

Essex Eagles

Captain: Ryan ten DoeschateOverseas player: Jesse Ryder (NZ)Have never won the competition despite four appearances at finals day, including last year when they lost their semi-final to eventual winners Northants. The captaincy switches from James Foster to Ryan ten Doeschate for T20, while New Zealander Jesse Ryder - a sweet striker of the ball - may well enjoy both the small boundaries at Chelmsford and the local nightlife.Athers' one to watch: Jesse Ryder - Could fire or backfire. Essex are gambling on left-hander Ryder to give them some X-factor and swell what is an already impressively potent batting line-up.

Glamorgan

Captain: Jim AllenbyOverseas player: Jacques Rudolph (SA)Woeful T20 record over the years, failing to advance from the group stage since 2008 and last reached finals day in 2004. Hard to see how or why that will change this year given their squad remains largely the same apart from the addition of South African batsman Jacques Rudolph.Athers' one to watch: David Lloyd - Has the perfect name for T20 cricket! No relation to Bumble, this 21-year-old has perfectly-working knees as well as bags of potential if not experience. Keep your eye on him!

Gloucestershire

Captain: Michael KlingerOverseas player: Michael Klinger (Aus)A quarter-final appearance in 2012 is the only time they have emerged from the group stage in the last six years. On-field struggles are partly due to the financial constraints on the playing squad while their Bristol ground is redeveloped. Not much has changed much since last season, when they won only three T20 games and finished bottom of the now defunct Midlands/Wales/West division.Athers' one to watch: Michael Klinger - Averaged over 50 in 2013 but still could not drag his team out of the group stages; the Australian had another impressive Big Bash run with the Adelaide Strikers but has been rather short of runs so far this season.

We look back at Hampshire's dramatic win in the 2012 T20 final despite David Miller's heroic efforts for Yorkshire.

Hampshire

Captain: James VinceOverseas players: Kyle Abbott (SA), Glenn Maxwell (Aus)Strong T20 pedigree having been to finals day in each of the last four years, including triumphs in 2010 and 2012. The signing of Australian all-rounder Glenn Maxwell for a post-IPL stint adds an extra dimension and the bookmakers' like their chances of another big campaign, making them the pre-tournament favourites. The decision to give James Vince a chance to captain the side is an interesting one and the young batsman is planning an aggressive approach.Athers' one to watch: Glenn Maxwell - Loves to give it a wallop. His eye-catching form in the IPL has elevated him back amongst the elite after a modest campaign for Surrey last season in which he averaged just 17.75. Will miss opening games, though.

Kent Spitfires

Captain: Rob KeyOverseas player: Doug Bollinger (Aus)The Spitfires still set the standard for nicknames but the same cannot be said of their performances in this competition during the last two years. Rob Key, who led Kent to victory at Lord's in the 2008 final, returns to the captaincy after James Tredwell's reign ended after just a year. Left-arm seamer Doug Bollinger is in town all season as overseas pro and he has plenty of T20 experience in the IPL and for Australia.Athers' one to watch: Sam Billings - Showed short flashes of what he is capable of with the bat in last season's T20, the suspicion being there's more to come from this natural successor to Geraint Jones.

Middlesex Panthers

Captain: Eoin MorganOverseas players: Dan Christian (Aus), Chris Rogers (Aus)If you go to work wearing an all-pink outfit then you'd better be good at your job. Middlesex have the first part covered (the pink outfit) but haven't managed to advance from the group stage since winning the competition in 2008. Eoin Morgan gets the chance to captain the side, although his availability would be compromised by a Test recall, while the signing of no-nonsense Australian all-rounder Dan Christian - who once served a one-match ban for smashing up three dressing rooms in the same season - could be a master-stroke.Athers' one to watch: Steven Finn - Back in the wickets and firmly back in the minds of the England selectors, Finn will be a handful on most pitches. Will feel like a new signing for Middlesex after not playing in last year's competition.

Somerset

Captain: Marcus TrescothickOverseas players: Dirk Nannes (Aus), Alviro Petersen (SA)Powerful, deep, experienced batting line-up has made Taunton a T20 fortress and they have qualified from the group stage in each of the last five years. A fraught quarter-final defeat to Surrey at The Oval last summer meant they missed finals day for the first time since 2008. The addition of Australian left-arm quick Dirk Nannes adds something different to the bowling attack and should provide a potent combination with Alfonso Thomas in the 'death overs'. No trophy since winning this competition in 2005 despite regularly contending on all fronts.Athers' one to watch: Lewis Gregory - In a side heavy with experience, all-rounder Gregory offers an insight into the future and will be keen to repeat his form of 2012 when he took four-for against Essex in the quarter-finals.

Surrey

Captain: Graeme SmithOverseas player: Graeme Smith (SA)Have made slow start back in Division Two of the County Championship but have a squad packed with T20 talent. Kevin Pietersen is the headline attraction and his love of the big stage will be catered for at a packed Oval under the Friday night (flood) lights. Haven't won the tournament since the inaugural edition in 2003 and memories of a heavy defeat to Northants in last year's final still linger.Athers' one to watch: Kevin Pietersen - Desperately short of early-season runs, Surrey need a contribution of talismanic status from Pietersen to get back on track and make amends for last season's thumping final defeat.

Sussex Sharks

Captain: Ed JoyceOverseas player: Yasir Arafat (Pak)Won't be worse than last season when they lost all of their home games to end bottom of the South Group with just one win. The main casualties of that miserable showing are overseas duo Dwayne Smith and Scott Styris, neither of whom are returning. Instead, Pakistan all-rounder Yasir Arafat brings his T20 experience back to Hove for another spell with the county after playing for Somerset, Lancashire and Surrey in the past three summers.Athers' one to watch: Luke Wright - A rare talent - but one excluded from England's short-term limited overs plans. Must improve on his 2013 T20 return of one fifty and an average of 21.67 and chip in with more wickets.